There are a number of major exceptions to the requirement that officers need a warrant to search and seize one's possessions or to arrest a person. These exceptions include:

Consent. If a person consents, officers may search them or their possessions without a warrant.

Plain view. If, for example, an officer sees what appear to be marijuana plants growing in my front yard (or in the window of my house) the officer can seize those plants.

Exigent circumstances. This means emergencies. If an officer has reasonable cause to believe that I am going to hurt people around me, they can search me.

Motor vehicles. If officers have probable cause to believe there is something illegal in my car at a traffic stop, they may search. This is because cars are so mobile and the evidence could be taken away and destroyed.

Search incident to lawful arrest. If I am being legally arrested, I can be searched.